The validity and responsiveness of three quality of life measures in the assessment of psoriasis patients: results of a phase II study

BACKGROUND: Patient-reported outcome (PROs) measures are being used more frequently in investigational studies of treatments for moderate to severe plaque psoriasis. The objective of this study was to examine the relationships among the Dermatology Life Quality Index (DLQI), the Short Form 36 (SF-36), and the EuroQOL 5D (EQ-5D) and to assess their validity, responsiveness, and estimates of minimum important differences. METHODS: A Phase II, randomized, double-blind, parallel group, placebo-controlled, multi-center clinical trial assessed the clinical efficacy and safety of two doses of subcutaneously administered adalimumab vs. placebo for 12 weeks in the treatment of 147 patients with moderate to severe plaque psoriasis. This study provided the opportunity to evaluate the validity and responsiveness to change in clinical status of PROs instruments. Patients completed the DLQI, SF-36, and EQ-5D questionnaires at baseline and at 12 weeks. Blinded investigators assessed the Psoriasis Area and Severity Index (PASI) scores and the Physician's Global Assessment (PGA) scores of enrolled patients. The responsiveness of the measures to changes in the clinical endpoints from baseline to Week 12 was assessed. Estimates of minimum important differences (MID) were derived. All analyses were performed with blinded data; findings and conclusions were not biased based on treatment condition. RESULTS: The dermatology-specific DLQI was highly correlated to clinical endpoints at baseline and at Week 12, and was the most responsive PRO to changes in endpoints. Compared with the SF-36, the EQ-5D index score and VAS scores were generally more highly correlated with clinical endpoints, but displayed about the same degree of responsiveness. The most responsive SF-36 scales were the Bodily Pain and Social Functioning scales. Estimates of the MID for the DLQI ranged from 2.3–5.7 and for the SF-36 Physical Component Summary (PCS) score ranged from 2.5–3.9. CONCLUSION: This study provides support for the continued use of the DLQI and SF-36 PCS in the assessment of treatments for psoriasis. On the basis of the results from this trial, the EQ-5D should be considered as a general PRO measure in future clinical trials of patients with moderate to severe plaque psoriasis.